Oscillographic method of and system for spectrographic analysis



Aug. 30, 1949. e. H. DIEKE OSCILLOGRAPHIC METHOD OF AND SYSTEM FOR SPECTROGRAPHIC ANALYSIS 2 Sheets-Sheet 1 Filed Feb. 18, 1947 Wm/M/% A TTORNE VS G. OSGILLOGRAPHIC METHOD OF AND SYSTEM FOR SPECTROGRAPhIC ANALYSIS H. DIEKE Aug. 30, 1949.

2 Sheets-Sheet 2 Filed Feb. 1.8, 1947 Br Mix/W4 ATTORNEYS Patented Aug. 30, 1949 UNITED STATES PATENT OFFICE OSCILLOGRAPHIC METHOD OF AND SYSTEM FOR S PECTROGRAPHIC ANALYSIS Gerhard H. Dieke, Baltimore, Md. Applieation Februal-y 18, 1947, Serial No. 729,272

13 Claims. (01. 315-2 Thisinvention relates to spectrochemical analysis and particularly to systems and methods suited to needsof industry where speed and simplicityoi operation are of greater importance than extreme accuracy.

l'Ihe present most commonly employed method of spectrochemical analysisinvolves the use of a photographic plate which isexposed to the spectrum produced by an are or spark discharge between electrodes of material whose composition is to be determined. Aside from variable factors, such as non-uniform sensitivity of photographic .platesand films, the temperature, concentration and 'age ofthe developing solution and action of the fixing bath, all of which afiect its accuracy,

the photographic method has the further disadvantage that arelatively long time is needed for the 'de'velopment, washing and drying of the photographic plate or film. Because of inherent slowness of the photographic method, it is not suited for close control of the composition of a ,furnace charge or melt, for example, or for other industrial processes where time is of essence either because of production demands or because the material analyzed substantially changes in composition between time of withdrawal of a sample of it for analysis andthe time when th .results of the analysis are available.

In accordance with the present invention, the spectrochemical analysis of a sample is effected substantially instantaneously by impressing the radiation from selected lines of the spectrum upon a corresponding number of photoelectric "cells which, in predetermined sequence, are rapidly and recurrently connected to an oscillograph. The intensities of the lines and therefore the concentrations of, the corresponding elements may be read directly from the resulting visual pattern, or alternatively, the deviations from standard concentrations may be determined by noting the extents to which it is necessary to adjust calibrated coupling networks of the tubes in order to make the visual pattern match with a standard pattern.

t More particularly and in one form of the invention, the photocells are successively connectfed, -1'or example, to the vertical-deflection circuit of a cathode-ray tube during each traverse vertically of the screen is indicative of the concentration of that element.

In another form of the invention, the photocells are sequentially connected to the verticaldeflection circuit as before but no sweep voltage is applied to the horizontal-deflection circuit. Instead, there is connected thereto one of the photocells which vie ws that one of the spectrum lines selected as a reference. Assuming the light source and the current supply for the tubes are steady, the resultant pattern is a series of vertically spaced spots each having a position which depends upon the respective intensities of the reference spectrum line and a particular one of the other selected lines. 1 If the light source and/or the current source for the cells are unsteady, the spots are more or less elongated traces; all, however, directed toward a common point if the couplingnetworks of the tubes are selected or adjusted to have the same timeconstant. The slope of a selected trace then corresponds with the relative intensities of the corresponding spectrum lines notwithstanding the aforesaid unsteadiness of the light source or power supply.

The invention further resides in methods and systems having features herein disclosed and claimed.

For more detailed understanding of the invention and for illustration of preferred forms thereof, reference is made to the accompanying drawings, in which:

Fig. 1 schematically illustrates a spectrographic analyzer jusing phototubes and a conventional cathode ray oscillograph or oscilloscope;

Fig. 2 is a detail view of an external sweep generator;

Figs. 3A-3D are examples of patterns obtained .with the system of Fig. 1;

Fig. 4'illustrates a modification of the system of Fig. 1; and

Figs. 5A -5D are examples of patterns obtained with the system of Fig. 4.

Referring to Fig. 1, the tubes l0l3, each associated with one of the slits !4il, are disposed along the focal curve of the spectrum produced by a light source, for example, an arc whose electrodes are comprised of material to be analyzed. Each cell is disposed continuously to view a selected line or region of a spectrum to be analyzed. Assuming it is desired to analyze steel samples for their copper, manganese and chromium contents, a spectrum line of each of those elements is selected and also an iron line to serve as a reference line. For example, the cells Ill-I3 may be disposed respectively to View the spectrum lines zontal-deflection circuit, the output Tof one of theposition I) of the cathode spot, for example, to-

ward the left and below the center of the screen, so that the maximum area of the screen is usable rather than merely one-quadrant.

Typical patterns resulting from this mode of connection to the deflection circuits of the oathode-ray tube are shown in Figs. A-5D, respectively, corresponding to Figs. 3A-3D. As in this instance, Figs. 5A-5D, the chromium line is absent, the contact on resistor I9 is adjusted to its zero position. In. this system, and as apparent from Figs. -5A-5D, the intensities of each of the lines viewed by the phototubes is plotted as a vertical-deflection against the concurrent horizontal deflection due to phototube or cell I3; that is, the measurement is that of the relative intensity of the line viewed by the cell Hi to that of the lines viewed by each of the'other cells in succession.

I With this arrangement, if the light source remains constant, the intensity of each of the spectrum lines corresponds with a spot appearing on the cathode-ray screen 40 and all spots lie on the same vertical line. If the source fluctuates, each of the spots moves along a line going through the common zero or origin point 0. When the networks l923 to 22-26 have equal time constants, each of these points moves along a straight line directed towards the origin 0 and the slope of each line is therefore a measure of the intensity of the spectrum and concentration of the corresponding particular element. Alternatingcurrent light sources commonly available can therefore be used with the system of Fig. 4 whereas this would ordinarily be impossible with the system of Fig. 1. 7

When the time constants of the severalcoupling networks have been adjusted or selected to effect equality, this relation is not upset by adjustment of the adjustable contacts of the resistors Hi to 22 effectively to vary the signal gain from the photocell to the oscillograph, providing that the resistors are used as potential dividers, as shown, rather than as rheostats.

The relative intensities or concentrations may be read directly from the cathode-ray screen 40, Fig. 4, or from a suitable angularly graduated transparent scale 58 attached thereto or disposed in front of it. Alternatively, a standard pattern on a transparent sheet may be disposed in front of the cathode-ray screen and the contacts of the several resistors l9-22 adjusted to effect match of the actual pattern therewith, the deviation of the concentration of the several elements then being read directly from scales associated with the several resistors. In either case, the concentrations can be read to within five per cent accuracy or better, comparable with that obtained by the much slower photographic method.

If a complete analysis is required for a sample having many constituents, the pattern on the screen becomes too complicated to be easily interpreted. However, even under such condition, the traces of the several elements can be identified by pulsing them at different characteristic rates.

In both systems, Figs. 1 and 4, the photoelectric tubes III to I! are preferably of the photomulti- 6 plier type, such as the IP 28, 931A and the IP 21 tubes manufactured by the Radio Corporation of America, because of their high sensitivity and linear response characteristic.

It shall be understood the invention is not limited to the particular systems disclosed and that changes and modifications may be made within the scope of the appended claims.

What is claimed is:

1. A system afiording substantially instantaneous analysis of selected lines of a spectrum comprising photocells for respectively continuously viewing said selected lines of the spectrum, an oscillograph, and switching means for connecting said cells to said oscillograph in rapidly recurring sequence to produce a pattern concurrently showing the intensities of said lines.

2. A system aifording substantially instantaneous analysis of selected lines of a spectrum comprising photocells for respectively continuously viewing said selected lines of the spectrum, an oscillograph including a cathode-ray tube, a sweep generator in circuit with one pair of deflection plates of said tube, and switching means operating in synchronism with said sweep generator sequentially to connect said cells in circuit with another pair of deflection plates of said tube.

3. A system afiording substantially instantaneous analysis of selected lines of a spectrum comprising photocells for respectively continuously viewing said selected lines of the spectrum, an oscillagraph including a cathode-ray tube and a sweep generator in circuit with one pair of deflection plates thereof, switches each in circuitwith one of said cells and the other pair of deflection plates of said tube, and motor-driven cam structure for actuating said switches sequentially to connect said cells to said other pair of plates each for a predetermined portion of the cycle of said generator.

4. A system affording substantially instantaneous analysis of selected lines of a spectrum comprising photocells for respectively continuously viewing said selected lines of the spectrum, resistance-capacitance networks respectively in circuit with said photocells, an oscillograph having a horizontal-deflection circuit and a verticaldeflection circuit, a generator for introducing a sweep voltage into one of said deflection circuits, and switching means operating in synchronism with said generator sequentially to include in the other of said deflection circuits voltages respectively derived from said networks.

5. A system affording substantially instantaneous analysis of a spectrum comprising photocells for respectively viewing selected lines of the spectrum, an oscillograph having a horizontaldeflection circuit and a vertical-deflection circuit, a generator for introducing a sweep voltage into one of said deflection circuits, and switching means operating cyclically in syn-chronism with said generator sequentially to connect said cells to the other deflection circuit and in each cycle to apply a voltage establishing the base line of the pattern resulting from aforesaid sequential connection of the cells.

6. A system affording substantially instantaneous analysis of a spectrum comprising photocells for respectively viewing selected lines of a spectrum, an oscillograph having a horizontaldeflection circuit and a vertical-deflection circuit, switching means for connecting said cells sequentially to one of said deflection circuits, and means for connecting a selected one of said cells to the other of said deflection circuits.

"7. A system afiord-ing substantially instantae neous: analysis. of a spectrum comprising photocells for respectively viewing selected lines. of: a spectrum, resistance-capacitance networks re,- spectively incircuit with said. phetocells, an oscillograph having horizontal-deflection and vertical-deflection. circuits, switching means. in predetermined and rapidly recurring sequence introducing into one of said deflection circuits voltages respectively derived from said networks, and means for introducing into the other oi said deflection circuits a voltage derived: from a selected one of said networks.

8. A system affording substantially instantaneous analysis of a spectrum. comprising photocells for respectively viewing. selected lines. of a spectrum, an oscillograph having horizontal. and vertical-deflection circuits, and switching means operating cyclically to connect said cells in rap.-

idly recurring sequence to one of said deflection circuits and in each cycle to apply a voltage. estal'llishing the base line of'the pattern resulting from aforesaid sequential connection of the cells, and. means for connecting one of said cellstothe other of said deflection circuits.

9; The method of spectrochemically analyzing a specimen which comprises the steps of continuously producing voltages respectively corresponding with the intensities of selected regions of" the spectrum of the specimen, and repeatedly and in predetermined sequence applying said voltagesto an clscillograph.

10. The method of spectrocherni cally' analyzing a specimen which comprises the steps-of continuously producing voltages respectivelycorresponding with the intensities of selected regions ofthe spectrum of the specimen, applying a periodic sweepvoltage to one deflection circuit oi an oscil lograph, and insynchronism with saidsweep voltage repeatedly applying said first named voltages in predetermined sequence to another deflection circuit of said oscillogra-ph.

11. The method of spectrochemically' analyzing cells; each associated. with a spectrographic slit for respectively continuously viewing selected lines at a spectrum, potentiometers respectively in circuit with said photocells, an oscill'ographl, and switching. means for connecting: the adjustable contacts: at saidpotentiometers to: said oscillograph; in rapidly recurring sequence to product a. pattern. determined by the intensities. of said lines and the setting of. said contacts.

13.. The; method 02 spectrochemically analyzing a specimen which comprises; the steps of continuously producing voltages respectively corresponding with the intensities of selected regions, of the spectrum of said specimen, repeatedly and: sequentially applying a selected fraction of: each of said voltages to. an oscillograph, and varying the; fraction. of: the. individual voltages which is appliedto said oscillograph to match the actunla oscillograph. pattern with a standard patterm.

GERHARD'IL DIEKE;

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